Electron discharge devices



June 5, 1962 .1 T. BALKWILL ETAL 3,037,833

ELECTRON DISCHARGE DEVICES Filed June 29. 1960 QMMVLW I //V VENTOFPS JOHN 7775/4606 BA'LKW/LL JA EJ FPOEEFPT HEJ HTTOP/VEY United States Patent 3,037,833 ELECTRON DISCHARGE DEVICES John Treagus Balkwill, Harlow, and James Robert Folkes,

Enfield, England, assignors to Associated Electrical Industries Limited, London, England, a British company Filed June 29, 1960, Ser. No. 39,541 Claims priority, application Great Britain July 6, 1959 3 Claims. (Cl. 316-18) The present invention relates to electron discharge devices and in particular to methods of manufacturing types of said devices which include electrodes having surfaces formed from materials which must be prevented from contaminating other surfaces within the device and cannot be heated to high temperatures.

During the manufacture of certain types of electron discharge devices, in particular image intensifiers, it is necessary to form electrodes having sensitive surfaces, for example, photo cathodes. Such a surface is formed by coating the surface of the electrode with a suitable material. One such material may be antimony. It is necessary to apply this coating by a vacuum deposition process when the electrode is in an evacuated chamber. Caesium vapour can then be introduced and the required portions of the surface of the electrode can be coated so that the electrode is formed into a photo emissive cathode.

If other electrodes of the device are exposed to the caesium vapour, the vapour will be deposited thereon with undesirable effects. The caesium contaminates the surface of the other electrodes in an undesirable manner, and may result in positive caesium ions being produced during the operation of the discharge device.

-It is also necessary in certain methods of manufacture to bake the evacuated chamber of the device at a high temperature, and the photo sensitive electrodes may not be able to withstand heating to a high temperature.

The object of the present invention is to provide a method of manufacturing electron discharge devices of the type described, which substantially prevents damage to sensitive surfaces of electrodes within the device.

According to the present invention a method of manufacturing an electron discharge device comprises the steps of connecting a subsidiary chamber to the envelope of said device by a long duct having a small cross-sectional area, inserting a component into said subsidiary chamber, evacuating said subsidiary chamber and said envelope, introducing a contaminating vapour into said subsidiary chamber so as to coat the surface of said component, the narrow cross-section, of the duct preventing appreciable flow of the vapour from the subsidiary chamber into the envelope, transferring said component along said duct into said envelope, and sealing up said duct at a point adjacent to said envelope.

The envelope and the components contained therein may be baked at a high temperature before any heat sensitive components are transferred from the subsidiary chamber into the envelope.

The duct is conveniently a glass tube having a crosssection which approximates in size to the cross-section of the component.

The component may be a frame supporting a screen which is to be formed into an electrode for an image intensifier.

The contaminating vapour may be caesium vapour.

In order that the invention may be more readily understood reference will now be made to the accompanying drawing in which the single FIGURE is a cross-sectioned plan view of an electron discharge device.

With reference to the FIGURE, an electron discharge device is formed with a glass envelope 1 containing an 3,037,833 Patented June 5, 1962 ice electron gun 2 and other electrodes 3, 4, 5 and 6 displaced along the envelope and adapted to be connected respectively to suitable sources of electric potential. The electron discharge device may be an image intensifying tube of the type in which an image carrying beam of radiation, for example visible radiation or X-rays, is inciiient on the end wall 7 of the envelope through a suitable ens 8.

The envelope also contains electrodes which may for example be fluorescent screens, photo emissive electrodes, photo conductors, secondary emitting electrodes, or any of the electrodes used in image intensifiers of the types well known in the art. Each of these electrodes is formed with at least one surface which has a sensitive coating. One such coating, for example, is formed by depositing a layer of caesium onto an antimony base. This form of coating must be applied to the antimony base in an evacuated chamber, and since caesium contaminates other surfaces it is essential that the caesium should not be deposited on the surface of other electrodes within the envelope of the electron discharge device.

During the manufacture of the device it may be necessary to bake the envelope 1 after it has been evacuated in order to remove all traces of gas from within the envelope. Some of the sensitive surfaces of the electrodes may not be able to withstand the heat of baking and therefore must be protected therefrom.

The envelope 1 may be evacuated through the duct 9. The envelope is connected to a subsidiary chamber 11 by a long duct 12 which has a narrow cross-sectional area, and is conveniently rectangular in cross-section. The duct 12 is sealed at each end respectively to the envelope 1 and the chamber 11, communicating with the envelope and the chanrber respectively through apertures 13 and 14. The aperture 14 may be closed with a metal flap 15 which is pivoted at one end so that it can be swung away from the aperture 14.

The chamber 11 may be evacuated through the duct 16. The chamber is formed with a holder 17 for an electrode 18 which is to be formed with a sensitive coating. The electrode 18 may be in the form of a thin screen. The electrode 18 is aligned with the duct 12 and is of such a size that it can be passed along the duct 12. The chamber 11 also includes containers 1'9 and 21 from which metal may be evaporated by heater wires 22, 23 extending outside the chamber, and a container 24 from which a luminescent material may be evaporated by a heater wire 25 extending outside the chamber. The containers 19, 21 and 24 are so positioned within the chamber 11 that materials evaporated therefrom can be deposited on one or both of the surfaces of the electrode 18 as required, in order to form the required sensitive coating or coatings on said electrode.

A ferromagnetic bar 26 is located in a recess 27 in the wall of the chamber 11 and has approximately the same cross-sectional area as the electrode 18 and hence can be passed along the duct 12.

The envelope 1 of the electrode discharge device is formed with a holder 31 adapted to hold the electrode 18 and may also be formed with a holder 32 for a second electrode 33 having one or more sensitive surfaces. The second electrode is aligned with a second narrow duct 34 along which the electrode may be passed and which connects the envelope with a second subsidiary chamber, similar to the chamber 11.

During the manufacture of an electron discharge device, the electrode 18 is located in the holder 17 in the chamber 11, and the containers 19, 21 and 24 are filled with materials as required. The envelope 1 and the chamber 11 are evacuated through their respective evacuating ducts. Sensitive coatings as required are then deposited on the surface'or surfaces of the electrode 18 by heating one or all the containers 19, 21 and 24 in succession or simultaneously. Heating any one of these containers provides a vapour, for example caesium, which deposits a layer of material on the-surface of the electrode 18. This vapour will not diffuse along the duct 12 into the envelope "1 because of the low pressure existing in the Whole evacuated system and the narrow cross-section of the duct 12. Hence the vapour Will not contaminate other surfaces in the envelope 1. The flap 15, if it is fitted, does not provide a gas tight seal between the chamber 11 and the duct 12 but it does tend to prevent diffusion of the vapour from the cham'berll into the duct 12.

The envelope '1 and its contents may have to'be baked in order to reduce the pressure therein to a very low value, and this may be done without baking the chamber 11 and its contents, since the chamber 11 is located at a distance from the envelope 1 and heat will not tend to travel-along the duct 12, particularly if the duct is made of glass. The electrode 18 within the chamber 11 is therefore not affected by the baking.

When the bakingis finished and the sensitive coatings have been applied to the surface of the electrode 18, the flap valve 15 is opened, either by tilting the whole apparatus or by a. magnet, a magnet is placed adjacent to the bar 26, outside the chamber 11, and the second magnet is moved causing the bar to move towards the electrode 18. This forces the electrode 18 into the duct 12 and therefore movement of thebar 26 causes the electrode to move along the duct 12 into the envelope 1, so that it is located in the holder 31 in the required position in the envelope 1. The electrode can be positioned close to theinner surface of the end wall 7 of the envelope. Hence an electrode having one or more sensitive surfaces formed by the de, posit of a contaminating material thereon is located in the envelope of the electron discharge device, a sensitive surface having been formed without contaminating other surfaces of the electrode structure, and without adversely ,afiecting-the surfaces of the electrode by baking it at a high temperature.

The second electrode 32 can be placed in a secondsubsidiary chamber of a similar construction to the chamber 11, and after treatment as described the second electrode can be moved along the duct 34 into position within the envelope 1.

After the electrodes have been moved along'the ducts into positions within the envelope '1, the ducts are sealed off at points close to the surface of the envelope so that the stubs do not project further-above the surface of the en-, velope than the stub end of the duct 9used for evacuating the envelope. .Hence the overall cross-section of the envelopeis not appreciably increased.

The methodand apparatus described enables an electron discharge device, in particular an image intensifier, to be manufactured with sensitive electrodes without the possibility of material used to form the sensitive coating on the electrodes contaminating other surfaces, and without the danger of adversely'affecting the sensitive surfaces by heating. The arrangement enables a'plurality of electrodes to be ,located adjacent to each other extending along the envelope, and enables one electrode to be located adjacent to the end wall of the envelope. Each electrode is treatedindividually in a secondary chamber and hence very good results can be obtained with this arrangement.

What we claim is:

l. A method of manufacturing an electron discharge device having an envelope adapted to contain at least one component comprising the steps of inserting said component ina subsidiary chamber which connects with said envelope, simultaneously evacuating said envelope and said subsidiary chamber, introducing a vapour into said subsidiary chamber so as to coat the surface of said component with a layer of a required material and substantially preventing said vapour frompassing into said en-. velope, transferring said component from said subsidiary chamber into said envelope without substantially altering the pressure in said envelope, and finally sealing off said envelope from said subsidiary chamber.

2. Apparatus for use in manufacturing an electron discharge device of the type having an envelope and means for supporting a component Within said envelope, said apparatus comprising asubsidiary chamber, means for supporting said component within said subsidiary cham ber, means for introducing a vapour into said subsidiary chamber so as to coat the surface of said component with a layer of a required material, a member having surfaces defining a long duct connecting said subsidiary chamber with said envelope, said duct having a cross-sectional area which is small compared-with the length of the duct so that substantially no vapour difluses along said duct from said subsidiary chamber into said envelope but which is large enough to allow said component to be passed along said duct, means for transferring said component along said duct from-said supporting means in said subsidiary chamber to said supporting means in said envelope, and means for evacuating said envelope and said subsidiary chamber simultaneously.

3. Apparatus for use in manufacturing an electron dis charge device of the type having an envelope and means for supporting a component within said envelope, said apparatus comprising a subsidiary chamber, means for supporting said component within said subsidiary chamber, means for introducing a vapour into said subsidiary chamber so as to coat the surface of said component, with a layer of a required material, a member having surfaces defining a long'duct connecting said subsidiary chamber with said envelope, said duct having a cross-sectional area which is small compared with the length of the duct so that substantially no vapour diffuses along said duct from said subsidiary chamber into said envelope but which is huge enough to allow said component to be passed along said duct, a flap hinged to said subsidiary chamber and adapted to cover the'end of said duct which connects with said subsidiary chamber,"means for transferring said component along said duct from said supporting means in said subsidiary chamber. to said supporting means in said envelope, and means for evacuating said envelope and said subsidiary chamber simultaneously.

References Cited in the file of this patent ,UNITED STATES'PAIENTS 

